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 A260626 a(n) = gcd(m, 2^m-1) where m is the n-th nonprime positive integer. 1
 1, 1, 3, 1, 1, 1, 3, 1, 1, 1, 9, 5, 7, 1, 3, 1, 1, 1, 1, 3, 1, 1, 1, 1, 9, 1, 1, 5, 21, 1, 1, 1, 3, 1, 1, 1, 1, 27, 1, 1, 1, 1, 15, 1, 7, 1, 1, 3, 1, 1, 1, 9, 1, 1, 1, 1, 3, 5, 1, 1, 21, 1, 1, 1, 1, 9, 1, 1, 1, 1, 1, 3, 1, 1, 25, 3, 1, 7, 1, 27, 11, 1, 1, 3, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS 2^m - 1 is a nonprime number if m is a nonprime number. LINKS Michel Lagneau, Table of n, a(n) for n = 1..10000 FORMULA a(n) = gcd(A018252(n), 2^A018252(n)-1). a(n) = A014491(A018252(n)). - Michel Marcus, Nov 01 2015 MAPLE seq(`if`(isprime(m), NULL, igcd(m, 2^m-1)), m=1..150); MATHEMATICA GCDnonPrime[n_Integer]:=GCD[2^FixedPoint[n+PrimePi@#&, n+PrimePi@n]-1, FixedPoint[n+PrimePi@#&, n+PrimePi@n]]; Array[GCDnonPrime, 120] GCD[#, 2^#-1]&/@Select[Range[200], !PrimeQ[#]&] (* Harvey P. Dale, Aug 25 2019 *) PROG (PARI) for(n=1, 1e3, if(!isprime(n), print1(gcd(n, 2^n-1)", "))) \\ Altug Alkan, Nov 01 2015 CROSSREFS Cf. A014491, A018252. Sequence in context: A060901 A351545 A087612 * A155828 A226203 A327791 Adjacent sequences: A260623 A260624 A260625 * A260627 A260628 A260629 KEYWORD nonn,easy AUTHOR Michel Lagneau, Oct 31 2015 STATUS approved

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Last modified February 6 03:21 EST 2023. Contains 360091 sequences. (Running on oeis4.)